This invention relates generally to screw-capping devices for automatically screw-tightening caps on containers such as bottles. More particularly, the invention relates to a screw-capping device which the operational action of grasping and releasing each cap by means of cap holding pawls is accomplished by utilizing air pressure.
In the past, various cap tightening devices for automatically tightening caps on containers such as bottles have been developed. The devices most generally used are of a type wherein each of a large number of cap holding heads, which ascend, descend, and rotate, grasps and picks up one cap from among many caps which have been fed with their open sides down onto a turntable and screw-caps the cap onto the open part of a container which has arrived at a position immediately below that head.
Among cap tightening devices of this type there is one (as disclosed in the specification of Japanese Patent Application No. 138,679/1977) wherein there are provided a rotating shaft rotated by suitable driving means and a cap holding cylinder having a plurality of cap holding pawls pivotally supported around a circle and having tooth edges at the inner side of the circle, an elastic ring member being stretched around the outer surfaces of the cap holding pawls thereby to impart thereto a force tending to thrust their tooth edges inward to grasp and hold a cap. Between the shaft and the cap holding cylinder, there is interposed a friction clutch to transmit rotation therebetween under torques below a certian predetermined value. Furthermore, a pressing member capable of ascending and descending in an air-tight manner is inserted above the cap holding pawls, and a pressurized air chamber for introduction of pressurized air thereinto is formed between the upper surface of the pressing member and the inner wall surface of the cap holding cylinder. When the pressurized air is introduced into this chamber, the pressing member is forced downward, and its lower peripheral part presses against the upper ends of the cap holding pawls thereby to spread and open the pawls and to release the cap.
In this device, however, compressed air for forcing down the pressing member as mentioned above is sent from the lower part of a support stem for rotatably supporting the cap holding cylinder directly from above onto the upper surface of the pressing member, the upper part of which is in sliding contact with a cylinder. When, upon completion of the tightening of the cap, pressurized air is supplied to force the pressing member down, and the cap holding pawls are spread and opened, the above mentioned cylinder is instantaneously pressed downward by the forcing down of the pressing member. Furthermore, since the cap holding cylinder and the part enclosing the friction clutch part are assembled integrally within the same housing, a reaction force arising from the opening of the cap holding pawls acts instantaneously on the clutch side.
As a result, the friction plates of the clutch, which have been in a slipping state after completion of cap tightening, are again pressed together, and the cap holding cylinder is again rotated to additionally tighten the cap, whereby the cap is excessively tightened.